I think that this is a great idea! One time I messed up a road, but there was no way in placing grass back 
! So I just had to go with it :’( and if I left it it would of tainted my world! A lot of people have already mentioned this though, here are a few links:
http://discourse.stonehearth.net/t/grow-back-the-grass/12476
http://discourse.stonehearth.net/t/grass-regrowth-replacement/16286
Now these are just two of the massive list! Please devs, please implement this idea! EVERYBODY WANTS IT!!